Fine-tunings in radiative $\alpha$-particle capture on $^{12}$C at astrophysical energies

TL;DR

This study uses cluster effective field theory to analyze the radiative alpha-capture on carbon at astrophysical energies, revealing extreme sensitivity to the electromagnetic fine-structure constant.

Contribution

It demonstrates that low-energy S-factor data tightly constrain variations in the fine-structure constant during this nuclear reaction.

Findings

Low-energy data restrict variations in alpha to less than 0.2 per mille.

Both E1 and E2 radiative captures are highly sensitive to alpha changes.

The reaction's astrophysical S-factor is tightly constrained by the data.

Abstract

We investigate the fine-tuning of radiative alpha-particle capture on carbon, $\alpha(^{12}{\rm C},^{16}{\rm O})\gamma$, at astrophysical energies. Utilizing results from cluster effective field theory for this reaction, we find that the low-energy data of the astrophysical S-factor allow for only very small variations in the electromagnetic fine-structure constant $\alpha$, namely $|\delta \alpha/\alpha| \leq 0.2\,$ per mille, in both the $E1$ and the $E2$ radiative capture.